I start with the assumption that they picked 100k miles for the base model over 8 years because 12.5k is near the average driver IIRC and because it's aligned with at least some of the competition.
For the ranges of the 40, 60, 85 kWh use the simple 55 mph numbers: 160 mi., 230 mi., and 300 mi.
1. Full cycles[SUP]*[/SUP] if you used 100% to 0%, recharged fully, and repeated for 40 kWh warranty: 625 cycles (100,000 / 160)
2. Corresponding distance for 60 kWh battery: 143,750 mi. (625 * 230)
3. Corresponding distance for 85 kWh battery: 187,500 mi. (625 * 300)
Why is the 60 kWh warranty "only" 125,000 mi.? They're baking in more wear and tear into the warranty expectations for the 60 kWh, partly because of the expectation of supercharger use.
Why is the 85 kWh warranty "unlimited"? Two reasons I suspect: (1) a bit of bonus slack in the battery on their top end size, (2) expectation that few drivers will be driving more than 23,437.5 mi./yr. (=187,500 / 8), (3) counterpoint to "range of warranty" anxiety, and (4) great PR.
So in short... the 40 kWh is likely getting the best deal, mathematically speaking.
[SUP]*[/SUP] The ratios work out the same whether you use 100% charge, 80% charge, 60% charge, etc. Using 100% is simplest.